1. Field of the invention
The present invention relates to the construction of jet headers for use in a system for aeration and/or mixing of water in basin or lagoon, and more particularly to a jet header of improved construction for use in such a system.
The term "wastewater" as used hereinafter, is intended to include any water of domestic, commercial and industrial origin. Other types of liquid mixtures may also be treated by such a system.
2. Brief description of the prior art
There are presently three types of jet aeration/mixing systems that are used industrially.
The first system which may be said to be of the "self-suction" type, includes jets that are so designed as to draw air or another gas at atmospheric pressure without any means of pressurization other than the dynamic pressure of the wastewater flowing through a pipe. In this system, the waterwater passes into a long venturi tube that is open to air, and is expelled as a jet containing air bubbles at the discharge end of the tube.
The second system includes jets fed by air or another gas under pressure, and by water under pressure. In this second system, the wastewater flows through a short venturi tube connected to a supply of air under pressure.
The third system include a jet designed to mix the content of a liquid tank, the liquid in the tank being used as motive pressure to feed the jet. A secondary fluid in gas or liquid form can be injected into the jet depending on the kind of mixing desired in the tank and whether or not a chemical reaction is also to take place such as, for example, neutralization, system equalization, floculation, etc.).
All of these types of jet aeration systems are supplied by a common source of pressurized wastewater flowing in a plenum water pipe, also called water header.
The above first two types of systems may utilize a common source of air flowing in a plenum air pipe, also called air header, if individual air intakes cannot be connected directly from the water surface to the venturi tube, for such reasons as ice protection, aesthetics, or life expectancy of the equipment. If there are no such reasons, then individual air intakes may be used, thereby making the resulting structure much simpler. This simplification is particularly advantageous with the jet aeration system of the self-suction type. In fact, the air supply can then be reduced to an individual short intake having a very small diameter, thereby avoiding the necessity of an air header running parallel to the wastewater header. In such cases, the only header necessary is therefore the water header which can be installed parallel to the water surface in the basin and very close to the water level. The elevation of this water header can vary indefinitely from deep submergence up to above the water surface.
Canadian patent application No. 561,448 filed on Mar. 15, 1988 and its counterpart U.S. Ser. No. 170,742 filed Mar. 21, 1988, now U.S. Pat. No. 4,857,185, both in the name of Gaetan Desjardins, disclose a system for the treatment of wastewater, comprising a combined air and wastewater header assembly extending across a basin. This assembly may be described as a group of pipings provided with means creating aerated water jets discharging into the basin and causing circulation of the wastewater in an endless path in this basin while simultaneously aerating it. A dam is formed across the path to allow sludges to settle at the bottom of the basin. A pumping station, built into a well, is used to feed the wastewater header with water drawn from the top of the body of wastewater in the basin; to aerate the water as it is discharged into the basin; to draw out sludges that have accumulated upstream of the dam; and generally to circulate water to clean the pipings whenever necessary.
It is well known by those skilled in the above summarized art that the construction of a jet aeration header like the one used in the system disclosed in the above identified patent applications or in any other wastewater aeration systems of the same type is time-consuming and therefore expensive.
Indeed, the construction of such a jet header requires the attachment and operative connection of at least one laterally extending, wastewater outlet conduit onto a pressurized wastewater pipe to produce a water jet flowing concentrically through a long or short venturi cone where it is subsequently mixed with air to form a mixture of water and gas bubbles that may be energically discharged into the basin.
Of course, this connection must be hydraulically efficient, so that the outlet conduit and its connection to the wastewater pipe have controlled internal surfaces in order to achieve trouble-free operation.
This major constructional requirement is usually achieved by using piping components made of fiberglass-reinforced plastic material (F.R.P.) because of the recognized properties in terms of molding characteristics, smoothness and corrosion resistance of this material.
Because the construction of such a jet header necessitates intensive manual work, the quality of the resulting headers may vary substantially from one another.
More over, it is known that any F.R.P. material consisting of fibers glued together by resin is difficult to work with. This problem is so well known that in most the industrialized government agencies have enacted specific F.R.P. construction standards to ensure a minimum quality level. In North America, these Standards are as follows:
Canadian Standard for F.R.P. corrosion resistant equipment # CGSB 41GP22 rev./84.
National Bureau of Standards of the United States # PS15-69.
For different reasons (mainly construction costs, difficulties in adapting the jet header construction to the above Standards etc . . . ), no jet aeration header presently available on the market today can easily meet those well established constructional requirements. To better respect these fabrication standards idealy each piece must be moulded to specification in one piece.
After these pieces are so moulded, no alteration should be permitted on these pieces. Only standard assembly should be allowed without altering the structure of these pieces by cutting or drilling through them.
One of the competitor construction methods presently used to connect wastewater outlet conduits to a main wastewater pipe consists in drilling large orifices on an existing F.R.P. pipe and fixing the outlet conduits onto these orifices. The main drawback of this method is that the F.R.P. pipe structure is seriously altered where its fibers are cut. As a result, the pipe cannot readily meet the construction requirements of the above mentioned Standards even if layers of reinforcing fibers are locally added around the conduits at their connections to the main pipe.
Another method that is presently used, consists in manufacturing directly the header by winding fibers around a mandrel on which prefabricated outlet conduits (i.e. jets) are already positioned to simultaneously form the pipe and outlet conduits projecting therefrom. In this method, the angle of orientation of the fibers is necessarily altered all around the jets and on pipe itself. As a result, the header which is so obtained does not and cannot meet one of the major requirements of the above Standards. According to this major requirement, the fiber winding angle must be kept uniform all along the pipe at a value of 55.degree..+-.2 degrees. The degree of orientation may varies for some construction but it must always remain constant within .+-.2 degrees maximum.
Thus, the above methods present two major construction deficiencies that are presently not overcome by any North American manufacturers. Indeed, the first method calls for a structural modification of a premolded F.R.P. pipe which is composed of fibers glued together with resin and has to be drilled to fix the jets. Of course, the portions of the pipe surrounding the jets may be reinforced but the resulting structure is almost impossible to be calculated as such. Moreover, it is presently very hard to perfectly position the jet inlets in front of the drilled holes and almost impossible to finish the internal surfaces of the connections to make them ultra smooth.
Presently, in spite of the recognized importance of quality control for this type of construction, no manufacturer can internally inspect the presently existing F.R.P. jet header. Such an inspection is impossible because of the size of the main pipe that is normally too small for anyone to crawl into. Yet, such a physical inspection is very important to ensure that any manual work is performed properly with no sharp edges or protusions on all internal surfaces and particularly at the jet connections. However, the possibility of a complete inspection is of the utmost importance in order to control clogging problems associated with poor jet connection construction. Indeed, if any pipe intersection is not matched and finished perfectly, sharp edges are left, to which fibers included into the wastewater will rapidly attach, thereby accumulating and pretty soon clogging the jet. Thus, any sharp edges will favor fibrous material to attach, accumulate and clog the jets.
Moreover, the second method mentioned hereinabove leads to pipes that do not meet the requirements of the above Standard with respect to the angle of orientation of the fibers, in addition to having the same disadvantages as the first method with respect to finishing and inspection of the resulting structure.